[TC] Consolidate TC withdrawals into one call

packages/tornado-cash/src/paymaster/fee.ts

@@ -19,6 +19,17 @@ interface UserOperationGasLimits {
 
 const ERC20_TRANSFER_GAS = 100_000n;
 
+// Execution-phase (callData) gas budgets used when a batch is consolidated into
+// a single userOp. Each extra deposit becomes a direct `pool.withdraw` call
+// executed by the ephemeral 7702 account — a groth16 verify plus the payout
+// (ERC20 pools add a token transfer to the sender). `FORWARD_GAS` covers the
+// final transfer of the accumulated balance to the recipient when the caller
+// supplied no tailCalls. These are conservative ceilings; the actual limits are
+// refined via bundler estimation when available.
+const PER_DIRECT_WITHDRAW_GAS = 400_000n;
+const PER_DIRECT_WITHDRAW_GAS_ERC20 = 500_000n;
+const FORWARD_GAS = 60_000n;
+
 const baseGasUnits: UserOperationGasLimits = {
   preVerificationGas: 80_000n,
   verificationGasLimit: 50_000n,
@@ -40,6 +51,30 @@ export function reasonableGasUnits(isERC20: boolean): UserOperationGasLimits {
   };
 }
 
+/**
+ * Gas units for a consolidated batch withdrawal (one userOp for the whole
+ * batch). deposit[0] is sponsored by the paymaster (its verify/payout stays in
+ * paymasterVerificationGasLimit, as in `reasonableGasUnits`); the remaining
+ * `extraWithdrawals` deposits run as direct `pool.withdraw` calls in the
+ * execution phase, so their gas belongs to callGasLimit. When the caller
+ * supplied tailCalls we keep the base callGasLimit as headroom for them;
+ * otherwise we only need the synthesized forward transfer.
+ */
+export function reasonableGasUnitsForBatch(
+  isERC20: boolean,
+  extraWithdrawals: number,
+  hasUserTailCalls: boolean,
+): UserOperationGasLimits {
+  const base = reasonableGasUnits(isERC20);
+  const perWithdraw = isERC20 ? PER_DIRECT_WITHDRAW_GAS_ERC20 : PER_DIRECT_WITHDRAW_GAS;
+  const executionTail = hasUserTailCalls ? base.callGasLimit : FORWARD_GAS;
+
+  return {
+    ...base,
+    callGasLimit: BigInt(extraWithdrawals) * perWithdraw + executionTail,
+  };
+}
+
 // The fee amount the paymaster expects to break even
 export function computeMinimumViableFee(reasonableGasUnits: UserOperationGasLimits, maxFeePerGas: bigint) {
 
@@ -68,10 +103,5 @@ export function computeMinimumViableFee(reasonableGasUnits: UserOperationGasLimi
   );
   const requiredPrefund = requiredGas * maxFeePerGas;
 
-  console.log("totalGasUnits", requiredGas);
-  console.log("maxFeePerGas", maxFeePerGas);
-  console.log("requiredPrefund", requiredPrefund);
-  console.log("multiply", 1.2);
-
   return multiply(requiredPrefund);
 }

packages/tornado-cash/src/paymaster/utils.ts

@@ -15,7 +15,7 @@ import {
   type BundlerClient,
 } from 'viem/account-abstraction';
 import { SIMPLE_7702_EXECUTE_ABI } from '../data/abis/account.abi';
-import { BuildSignedTornadoUserOpParams, SerializedAuth, SerializedUserOperation } from '../interfaces/user-ops.interface';
+import { BuildSignedTornadoUserOpParams, SerializedAuth, SerializedUserOperation, UserOpGasLimits } from '../interfaces/user-ops.interface';
 
 /**
  * EntryPoint v0.8 canonical Simple7702Account implementation. The ephemeral
@@ -91,6 +91,36 @@ export function ephemeralSenderAddress(privateKey: Hex): Address {
   return privateKeyToAccount(privateKey).address;
 }
 
+/**
+ * Bundler gas estimation (`eth_estimateUserOperationGas`) for an already-built,
+ * serialized userOp. Used to size a consolidated batch userOp — whose execution
+ * phase runs N-1 extra `pool.withdraw` calls — tightly instead of guessing. The
+ * op must carry a valid `paymasterData`/`eip7702Auth` so the bundler can
+ * simulate the paymaster's validation and the delegated execution.
+ *
+ * Not on viem's bundler action surface for our serialized shape, so we issue the
+ * raw request and parse the returned limits ourselves. Callers should treat this
+ * as best-effort and fall back to static limits on failure.
+ */
+export async function estimateUserOperationGas(
+  client: BundlerClient,
+  op: SerializedUserOperation,
+  entryPoint: Address,
+): Promise<UserOpGasLimits> {
+  const result = (await client.request({
+    method: 'eth_estimateUserOperationGas',
+    params: [op, entryPoint],
+  } as any)) as any;
+
+  return {
+    callGasLimit: BigInt(result.callGasLimit),
+    verificationGasLimit: BigInt(result.verificationGasLimit),
+    preVerificationGas: BigInt(result.preVerificationGas),
+    paymasterVerificationGasLimit: BigInt(result.paymasterVerificationGasLimit ?? 0),
+    paymasterPostOpGasLimit: BigInt(result.paymasterPostOpGasLimit ?? 0),
+  };
+}
+
 /**
  * Builds and signs a paymaster-sponsored withdrawal userOp for an ephemeral
  * 7702 sender, returning it serialized for the broadcast phase.